1. Field of the Invention
The present invention relates to apparatus and methods for collecting light from a Light Emitting Diode (LED) and transmitting it in a uniform manner.
2. Description of the Prior Art
LEDs are increasingly used in a number of devices as a light source. They are small and efficient, and last a long time. For example, several flashlights utilizing LEDs are available. See for example, U.S. Pat. Nos. 5,957,714 and 6,220,719, both having a common inventor with the present invention.
Devices that use LEDs as light sources generally include some method of collecting and/or focusing the light, as light from LEDs is diffuse. FIG. 1 shows a typical LED and the light it generates. A number of prior art devices include a combined reflector and refractor element to collect and transmit the light from an LED. See for example U.S. Pat. No. 5,898,267.
Most devices include optics which image the LED onto a plane in front of the LED. However, with devices such as flashlights, what is desired is not an image of the LED, but rather a column of uniform light.
Some prior art references appreciate this point. For example, a number of known devices use an array of LEDs, and often an array of lenses, to generate a column of light rather than a point source. See for example U.S. Pat. No. 6,283,613.
A need remains in the art for apparatus and methods for providing concentrated uniform light from a single LED.
The present invention comprises three important elements:
(1) the LED;
(2) A conical reflector for collecting light emitted to the sides of the LED; and
(3) A lens specially designed to focus the collected light into a near-collimated beam.
The LED is generally a conventional LED of the kind having a base, a light element and a domed transparent plastic housing attached to the base and covering the light element. Such an LED produces a bright band of light at the apex of its plastic housing, because of total internal reflection inside the plastic. This light is generally wasted. The reflector has a highly reflecting inside surface. Preferably, the reflector is a cone with about a 70xc2x0 angle. This configuration redirects the sideband light from the LED forward.
The lens is specially designed and configured to focus the light directly from the LED and the light reflected from the reflector into a near-collimated uniform beam. The lens has two important features. First, it includes a flat spot in the center of each of its curved surfaces. This prevents the lens from imaging the LED emitter and forming a dark spot in the beam. Consequently, the lens projects a field of near-uniform light. Second, the curved surfaces are elliptical rather than spherical to catch and nearly collimate the quickly diverging light from LED.
The flat spots 4 are preferably designed according to the following equation:
0.05dxe2x89xa6sxe2x89xa60.1d,
where s is the diameter of the flat spots, and d is the distance from the front of the LED to the center of the lens. The flat spot produces a near-uniform beam, rather than an image of the LED (with light and dark spots) that is produced by a conventional lens.
The elliptical curvature of the two curved surfaces of the lens is required to catch and nearly collimate the quickly diverging light from the LED. Preferably, the major axis of the ellipse is less than 0.7 times the distance d. Finally, the distance between the center of the ellipses should be about s, the diameter of the flat spots.
In one example, the lens is formed of plastic, and thickness of the lens at an edge is about one third the thickness of the lens at the center. In this example, (d) is approximately 1 inch, the half thickness of the lens is about 0.24 inches, the half diameter (if the elliptical sides were extended to meet) is about 0.70 inches, and edge thickness of the lens is about 0.16 inches.